Promises made long ago can taste bitter, and not only when deliberate oversight or ill intent is involved. Yesterday's report from the cross-party joint committee on human rights, looking at how legislation affects asylum seekers, is a reminder of how experience can triumph over hope. "A floor, not a ceiling, for human rights," Labour's 1997 manifesto promised. Contrast that with yesterday's finding: "The government's treatment of asylum seekers...falls below the requirements of the common law of humanity and of international human-rights law."

In the report, documented cases show how ministers have made evidence-free policy which panders to media prejudice, and which last year left up to 20,000 asylum-seeking families without any means of support. "We have been persuaded by the evidence," it concludes, "that the government has indeed been practising a deliberate policy of destitution." Its words echo those of a Joseph Rowntree Charitable Trust report issued earlier this week.

But, ministers say, this is a policy that works. As life has been made near-impossible for asylum seekers, their number has fallen back below 1997 levels. Unfortunately for the triumphalists, there is no evidence that this is due to what the committee judges to be inhuman treatment - especially for refused asylum seekers awaiting deportation, who are left, banned from work, with £35 a week in vouchers to live on. It might simply reflect the world's trouble spots currently being a little less troubled.

One specific get-tough measure was to insist that asylum seekers were charged for medical care. Consequently, sick people do not seek help until they are desperate. Two days in intensive care costs the same as a whole year's HIV treatment. The committee asked the health minister Rosie Winterton if she had any records of how much had been recouped, or of how many bills had been sent out. She had not. In 2005 a scheme to encourage refused asylum seekers to leave the UK before enforcement of repatriation deprived 116 families of all support. Local authorities reported dire consequences, in particular for children, several of whom had to be taken into care. Yet there is no evidence that this encouraged families to return to countries that they had fled at such cost. The government has not even published its evaluation. It seems, the committee concludes, that this is not evidence-based policy but a back-of-the-envelope response to a batch of bad headlines.

This government boasts that its policy is guided only by what works. In this report the weakness of that mantra is laid bare. For no one can call a policy that denies fundamental rights to one small group in society - and institutionalises its vilification - a policy that works.